Re: Search unit reply by Udo Schlengermann:
Two effects cause unacceptable inaccuracies when checking large sized angle-beam-probes on the IIW calibration block (25 mm thick, 100 mm quadrant):
1. side-wall reflections have influence on the pulse shape, i.e. on the maximum echo. So the position of maximum echo amplitude will not necessarily be the one where the beam hits the quadrant surface radially.
2. depending on the frequency the near-field length of a large probe may be larger than the radius of the quadrant (100 mm). Then the maxium echo is disturbed by near-field interferences. So determination of the index point (and beam angle) may be not correct.
Contrary to the reply by Nigel Armstrong, I cannot recommend the use of two parallel 25-mm-blocks, because the interface between the blocks will still cause side wall reflections.
Because of these reasons European Standard EN 12223 on block no 1 allows for modifications (thicker blocks).
European Standard 12668-2 for verfication of probes in annex B for example shows a modification with a thickness of 100 mm.
If your probe has a nearfield in steel larger than 100 mm, you have to use special blocks with a radius larger than that nearfield. Only then the axis of the beam hits the quadrant suface radially at the point of maximum echo amplitude.
Manufacturer's verification has to use blocks with radius up to 200 mm , as required by EN 12668-2.
GE Inspection Technologies GmbH
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: Hi everybody,
: I just got my new search unit of one inch large but now I need to know if i can check my sound entry point with the IIW block "type one" and if not what should i do?
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